A gas turbine engine generally includes a fan and a core section arranged in flow communication with one another. Additionally, the core section of the gas turbine engine general includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air is provided from the fan to an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gasses through the combustion section drives the combustion section and is then routed through the exhaust section, e.g., to atmosphere. In particular configurations, the turbine section is mechanically coupled to the compressor section by one or more shafts extending along an axial direction of the gas turbine engine. Such gas turbine engines are commonly used in aircraft.
The fan includes a plurality of blades having a radius larger than the core section of the gas turbine engine. The fan and the plurality of blades are typically driven by one of the shafts. However, for efficiency reasons, it can be beneficial to have the plurality of blades of the fan rotate at a speed less than a speed at which the respective shaft is rotating. Accordingly, a power gearbox is provided in certain gas turbine engines to mechanically couple the fan to the respective shaft in such a manner that allows the fan to rotate at a slower and more efficient speed. The gas turbine engine additionally includes a lubrication system for providing lubricant to one or more portions of the gas turbine engine, such as sumps of the compressor and turbine sections of the core section and the power gearbox.
During wind milling of aircraft engines, the oil pumps are ineffective due to the slow rotor speeds. In some instances, the engines may be wind milling because of a primary oil pressure failure and subsequent engine shutdown. The wind milling elapsed time may be very long, e.g. around 180 minutes. During wind milling, the bearings and gears of the main shafts turn, but are not receiving any new lubrication. In a power gearbox with rolling element planet bearings, the bearing part of the planet system may be durable enough to survive wind milling, however, the teeth of the planet gear, sun gear, and/or ring gear may not survive during an extended oil off condition. Existing systems rely on auxiliary reservoirs or oil tanks and powered pump systems to ensure some oil circulation and lubrication of the various components. Such active systems, however, can be heavy, complex, and unreliable.
Accordingly, a gas turbine engine having a simplified passive lubrication system for the power gearbox during wind milling would be particularly useful. Thus, the present disclosure is directed to a passive lubrication system for the power gearbox of the gas turbine engine during wind milling that utilizes the “hidden oil” coating the walls of the gearbox during normal operation and, if necessary, supplemented by an auxiliary reservoir.